The school population in England is linguistically diverse; according to official data, over one million pupils do not speak English as their first language. All teachers are expected to support English as an additional language (EAL) development as part of their professional responsibility. At the same time, there has been little specific curriculum and assessment specification for EAL within the mainstream curriculum. In the first part of this chapter, I will provide a retrospective analytic account of the educational responses to linguistic diversity, since the publication of the Bullock Report in the 1970s, paying particular attention to the changing provisions and conceptualisations that underpin the "mainstreaming EAL" approach of the past 30 years. The discussion will include an examination of the particular ideological articulation of the notion of equality in education that has influenced this approach. In the second part, I will suggest that research concerned with EAL has been largely filtered through a "mainstreamed" lens that focuses on the ways in which teaching, learning and assessment issues can be explored from a process-oriented curriculum and classroom perspective. It will be argued that future development in EAL provision will benefit from critical research that takes account of alternative curriculum conceptualisations and language development models.